Excellent red phosphors of double perovskite Ca 2La MO 6:Eu ( M=Sb, Nb, Ta) with distorted coordination environment

Abstract

Double perovskite Ca 2LaSbO 6, successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P2 1/ n, which is isostructural to Ca 2La MO 6 ( M=Nb, Ta). Excellent red luminescence of Eu-doped Ca 2La MO 6 ( M=Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca 2La 0.6NbO 6:0.4Eu 3+, quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca 2LaMO 6 is attributed to highly distorted polyhedra of EuO 8 (low tolerance factor of the pervoskite), and large bond distances of La−O (low crystal field effect of the activator).